Buffer concentration in serums
I have a serum that’s about 15% surfactant, 25% oil and oil phase ingredients, and 60% water and water phase ingredients. The pH is naturally around 5.5, which is convenient because that’s also my target. It has been stable for well over 1 month. However, I’d still like to buffer the formula, and while buffering solutions was easy while working in a chemistry lab, I now need to be mindful of factors like skin feel, irritation…etc and use ingredients that people aren’t too scared of.
It looks like most people use citric acid / citrate or lactic acid / lactate to buffer their products (which also might give them some antimicrobial activity depending on the pH and concentration). I’m a bit surprised about lactic acid since it’s only a decent buffer below pH 5. However, I could probably use it since I don’t expect pH to change very much. If either ingredient causes problems with my formula, I’ll try diluted forms of strong acids and bases like HCl and NaOH.
I’m just curious to know what concentrations (in %, mM, or g/L) of citric acid and lactic acid are used in cosmetics as a buffer, rather than as an active ingredient, and what other buffers you all like to use. I know that buffer concentration depends on a lot of factors, but I’m just interested in typical ranges people use in cosmetics. Fyi, I use the following spreadsheet for acid-base chemistry, and I can share a link if anyone could find it useful.
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